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View Full Version : Upgraded alternator owners I need some advice



lalojamesliz
02-26-2011, 09:27 AM
Can you guys tell me what voltage a st185 or 3sgte's voltage should be when it's just idleing at 800 rpm with the heater on high, headlights on and your pressing the brakes? I installed my so called 140 amp alternator but the volts droped to 12.2 when I had all those on but when the rpm's passed 1100 then the voltage is 14.2???? Is that normal or do I need to get a refund? Lastly, were did you guys buy your alternator at? If the one I have is crap I would want to buy one from a seller/place that has a good reputation. BTW All of my connections are good

klapa
02-28-2011, 04:51 PM
Can you guys tell me what voltage a st185 or 3sgte's voltage should be when it's just idleing at 800 rpm with the heater on high, headlights on and your pressing the brakes? I installed my so called 140 amp alternator but the volts droped to 12.2 when I had all those on but when the rpm's passed 1100 then the voltage is 14.2???? Is that normal or do I need to get a refund? Lastly, were did you guys buy your alternator at? If the one I have is crap I would want to buy one from a seller/place that has a good reputation. BTW All of my connections are good

That may or may not be "normal" - though I would think it IS normal.

A 140 AMP alt should be no different than even a 90 AMP alt as far as the voltage is concerned unless it is really loaded. Even with all the lights, blower, and ignition load I would not think it would not be loaded much over maybe 90 AMP - estimating 40 AMP each for the lights and blower motor (a very large estimate) and 10 AMP for ignition and other engine electronics. The voltage regulator will set the maximum output around 14.5V so long as the alt is spinning fast enough to deliver the required current load. If the alt is not spinning fast enough then you are running on your battery.

Of course - a 140 AMP alt would differ from the 90 AMP alt in that it has larger wire in the rotor windings and CAN deliver that current at the regulated voltage - WHEN it is spinning fast enough.

If you wanted to see if your 140 AMP alt is really any different from a stock alt you would need to measure the resistance of the rotor winding and compare between the two - to do this you would need access to the slip rings. Also - both resistance readings would very VERY small - so you would need a quality DMM with the capability to zero out the meter lead resistance.

You might also load the alt with some parasitic load to test it, as opposed to checking the winding resistance.

In my experience with cars - all of them are "running off the battery" at idle - they only charge the battery and feed the load at RPMs greater than 1500 or so.

lalojamesliz
03-03-2011, 06:10 AM
Damn, sorry klapa I forgot about this thread. The thing that's bothering me is the dimming headlights and other stuff when I come to a stop and since I drive with my lights on mabey 75% (in city) of the time I use my car it gets annoying and my battery isn't charging enough according to the shop that tested/charged my battery. I recieved my replacement alternator today but I wasn't able to install it. I'll take care of that in the morning when I get off from work. What makes me mad is the 70 amp alternator I had on held the voltage better during idle and with loads

klapa
03-03-2011, 04:29 PM
Damn, sorry klapa I forgot about this thread. The thing that's bothering me is the dimming headlights and other stuff when I come to a stop and since I drive with my lights on mabey 75% (in city) of the time I use my car it gets annoying and my battery isn't charging enough according to the shop that tested/charged my battery. I recieved my replacement alternator today but I wasn't able to install it. I'll take care of that in the morning when I get off from work. What makes me mad is the 70 amp alternator I had on held the voltage better during idle and with loads

I guess I did not read well enough!

Yea - if the lights are dimming with the new alt and not with the old then something is wrong - assuming the pulley is the same diameter between the two alts and you have good cable/connections on both ends of the large wire from the alt to the battery.

lalojamesliz
03-03-2011, 10:16 PM
My lights dim with both of the alternators that's why I bought a higher amperage one. Well it's supposed to be. I already got my replacement from the seller I bought my upgraded one from and I'll install it within the next couple of hours so I'll see how that one works.